1. Field of the Invention
The document EP-A-0337040 published Oct. 18, 1989 discloses a device for compensating a vibrational force F generated by a body. The device comprises four eccentric rotating weights located in a common plane P containing the centre of gravity of said vibrating body. Each weight is driven by an electric motor. The rotation axes of the weights are parallel to each other, perpendicular to the plane P and fixed with respect to said body. The four weights comprise a first pair of contrarotating weights whose rotation axes are symmetrical relative to a plane P.sub.1 containing the centre of gravity of said vibrating body and perpendicular to the plane P and a second pair of contrarotating weights whose rotation axes are symmetrical relative to said plane P.sub.1. The four weights rotate at the same angular frequency .omega.. The weights of the first pair each generate a rotating force F.sub.1 located in the plane P and comprising a sinusoidal unwanted first component about an axis perpendicular to the plane P.sub.1 and a sinusoidal wanted second component about the axis .DELTA. defined by the intersection of the planes P and P.sub.1 coincident with the line of application of the force F. The unwanted components of the rotating forces of said first pair compensate each other out and the wanted components are in phase and of the same amplitude. The weights of the second pair also generate two rotating forces located in said plane P and each having a sinusoidal unwanted first component about an axis perpendicular to the plane P.sub.1 and a sinusoidal wanted second component about said axis .DELTA.. The unwanted components of the rotating forces of said second pair compensate each other out and the wanted components are in phase with each other and of the same amplitude and phase-shifted by an angle 2.theta. relative to the wanted components of the rotating forces of the first pair. At least one accelerometer on each pair is connected to a real time computer adapted to calculate estimated values of the frequency, amplitude, phase and any variation in frequency by means of a non-linear self-adapting filter and to control the four motors by means of signals produced by angular encoders disposed on each of said motors.
The same document discloses a device for compensating a vibrational torque generated by a body. The device comprises four eccentric rotating weights rotating at the same angular frequency .omega., each weight being driven by an electric motor. The rotation axes of the weights are parallel to the moment vector of the vibrational torque to be compensated and fixed with respect to said body. The four weights comprise a first pair of weights rotating in the same direction in a common plane P.sub.2 and whose rotation axes are symmetrical relative to an axis D perpendicular to the plane P.sub.2 and a second pair of weights rotating in the same direction in a common plane P.sub.3 parallel to or coincident with the plane P.sub.2 and whose rotation axes are symmetrical relative to the axis D. The weights of the first pair generate two rotating forces F.sub.2 located in the plane P.sub.2 constituting a first torque whose moment vector is parallel to the axis D and whose modulus is sinusoidal. The weights of the second pair also generate rotating forces F.sub.2 located in the plane P.sub.3 constituting a second torque whose moment vector is parallel to the axis D and whose modulus is sinusoidal. The moduli of the first and second torques are out of phase with each other by an angle 2.theta..sub.1. At least one accelerometer on each pair is connected to a real time computer adapted to compute estimated values of the frequency, amplitude, phase and any variation in frequency by means of a self-adapting filter and to control the four motors using signals from angular encoders disposed on each of said motors.
In both devices, i.e. that for compensating a vibrational force F and that for compensating a vibrational torque, the self-adapting filter used in the real time computer is a Kalman filter which calculates estimated parameters of the excitation signal to be eliminated from the resultant residual signal .epsilon.(t).
The residual signal .epsilon.(t) is derived in a computer from acceleration signals .gamma..sub.1 and .gamma..sub.2 from the accelerometers.
The residual signal .epsilon.(t) is a signal of very low amplitude which can cause random operation of the system.
Given the form of the Kalman filter equations, the longer the time elapsed the less able is the filter to adapt to any changes in the excitation signal parameters.
An objet of the invention is to alleviate these drawbacks.